1. Field of the Invention
The present invention relates to an apparatus for destroying calculuses, of a type wherein a calculus present within a human body is disintegrated by externally applied energy.
A known apparatus for destroying calculuses comprises a generator for generating energy such as a focused shock wave or a focused ultrasonic wave, and an image processor for detecting the presence of a calculus existing within a human body and executing an appropriate processing for the purpose of breaking up the detected calculus. In operation, the apparatus searches for and detects a calculus within a human body, and upon detection of a calculus positions the focal point of destroying energy at the location of the detected calculus, and emits the destroying energy to disintegrate it. However, it is only a rare case that the calculus can be totally disintegrated by one application of the destroying energy. Normally the destroying energy is applied to the calculus repeatedly. However, during application of the energy, the human body respires, causing some body motion. Therefore, if the focal point of the radiated energy is set at where the calculus is first detected as being located, the calculus location, because progressing of the body motion, will become displaced from the focal point. Consequently, the radiation will then hit another part of the body, located off the affected part and possibly cause injury thereto.
A measure for overcoming the above problem is disclosed in Japanese Patent Disclosure No. 63-158049. In the technique disclosed, a period of an end portion in an expiration duration is detected since during this period, the affected part is only slightly displaced from the radiation focal point set. Thus, the expiration end period is used for the positioning of the focus of the radiation at the affected part, and for the generation of drive pulses for radiating the destroying energy, these pulses being generated repetitively at a preset rate (repetitive frequency). In other words, the calculus is disintegrated only during the expiration end period. When the drive pulse rate is, for example, 2 Hz, viz., the destroying energy is radiated every 0.5 sec., and the number of drive pulses that is required to disintegrate the calculus can be generated during the expiration end period. If the rate is lower than 2 Hz, for example, 0.5 Hz, that is, if the pulse is generated every 2 sec., the number of drive pulses generated during the expiration end period will be insufficient to produce enough radiated energy to disintegrate the calculus. It is assumed that the number of breathings is 12 per minute, a time of one breathing cycle is 5 sec., an expiration duration is 3 sec., and the expiration end period is 2 sec. In this instance, if the drive pulse rate is 0.5 Hz, this may give rise to an extreme case in which all the pulses required for disintegrating the calculus can not be generated during the expiration end period of 2 sec.
In particular, when the starting time point of the expiration end period is not coincident with the time point of generation of the first drive pulse, the number of pulses generated during the end period will be reduced.
Another example of prior art is found in the catalog of an extracorpreal urinary-passage stone lithotripsy device named "LITHOSTAR" manufactured by SIEMENS of West Germany. The catalogue describes a technique wherein shock waves are generated during a breathing gate in synchronism with the ECG in an electrocardiogram. However, it is not set forth in the catalog that the shock wave is generated in synchronism with a start point of the breathing gate. Therefore, there is the possibility that the calculus will move, due to body motion caused by breathing, from the focal point of the radiated breaking energy, and hence the energy will be applied to and adversely affects tissue near the calculus.
2. Summary of the Invention
Accordingly, an object of the present invention is to provide an apparatus for destroying calculuses and which is capable of generating drive pulses of a destroying energy within a predetermined period regardless of the preset rate for generating the drive pulses, and hence is free from the problem of injury possibly being caused to an unaffected part of the body by the mishitting of the destroying energy.
To achieve the above object, there is provided an apparatus for destroying calculuses comprising means for generating focused destroying energy, means for positioning a focus of the destroying energy at the position at which a calculus is located within the human body, means for detecting a radiation period of the destroying energy, means for generating a first drive pulse to drive the destroying energy radiation at a time point coincident with a start point of the radiation period, the first drive pulse generating means being coupled with the radiation period detecting means; and means for generating, during the radiation period, a train of drive pulses to repeatedly generate destroying energy at a predetermined rate, in succession to generation of the first drive pulses.
With such an arrangement, a first drive pulse is generated at a start point of a predetermined period, and a train of pulses is generated in succession within the same period. Thus, generation of the required number of drive pulses during the predetermined period is assured regardless of the pulse rate. Therefore, the problem inherent in the prior art, i.e. that the destroying energy hits another unaffected part of the body located near the affected part, with possibly adverse affects, is successfully overcome. Additionally, the present invention allows a speedy treatment to be realized.